Conventionally a component mounter has been used in the case of mounting electronic components on a printed board. This component mounter includes a mounting head which is capable of holding an electronic component by vacuum suction and mounting the held electronic component onto a printed board, and an XY robot which is capable of moving the mounting head two-dimensionally.
This component mounter mounts electronic components on a printed board in the following manner. Its mounting head gets a supply of an electronic component from a component supply unit and holds the supplied electronic component. Its XY robot conveys the mounting head, on which the electronic component is suction-held, above the printed board. The mounting head mounts the electronic component onto the printed board.
It is common that electronic components are respectively placed in the storage spaces, of the component supply unit, which are slightly bigger than the electronic components. The positions and angles of the electronic components vary slightly depending on the electronic components. With a purpose of mounting these electronic components on a printed board with high accuracy, the component mounter is configured to: pick up an electronic component using the component supply unit to; profile the shape of the electronic component using a non-contact position profiling unit (a so-called component recognition unit) such as a camera or a line sensor; correct a misalignment of the position or angle of the electronic component in the component supply unit; and mount the electronic component onto a printed board.
A method of profiling the position of a component by projecting a beam of laser light on the component and recognizing the shadows of the electrodes and the component is employed as a non-contact position profiling method for many types of mounters. However, in the case where there is a defective electronic component, for example, an electronic component including an upwardly-rising lead or a chipped or lost ball, it cannot be connected with a printed board correctly. In these days, in order to improve mounting quality further, there has been a demand to inspect components for an upwardly-rising lead and a chipped or lost ball, using a non-contact position profiling unit before the components are mounted.
Therefore, a component mounter is equipped with a line sensor which profiles the shape of an electronic component held by a mounting head three-dimensionally. First, the mounting head gets the electronic component from a component supply unit and holds the supplied electronic component. Subsequently, the line sensor profiles the holding status of the electronic component three-dimensionally and, when necessary, corrects the position of the electronic component before the electronic component is mounted. In addition, in the case where an electronic component has a defect in shape, it is possible to disregard the component using the mounter so that it is not mounted (for example, refer to Patent Reference 1: Japanese Laid-open Patent Application No. 2004-235671).
The line sensor is a device which projects a beam of laser light in a direction vertical to the moving direction of an electronic component held by a mounting head, detects the diffused light reflected on the surfaces of the electronic component by its detector, and profiles the shape of the electronic component three-dimensionally based on the triangulation theory.
There have been conventional line sensors structured to have two detectors which complement each other in the case where no reflected light returns to one of these detectors due to the angle of reflection. However, there are still some cases where the position of an electronic component cannot be corrected, depending on an electronic component. One is the case where the shape of an electronic component cannot be accurately profiled if a line sensor becomes incapable of profiling the shape of a component or if noises are overlapped. For this reason, the height of an electronic component in a generated image becomes unclear and thus it becomes impossible to recognize a misalignment of the electronic component. Another is the case where an acceptable component is judged as a defective component or a defective component is judged as an acceptable component because of an error in profiling the height of the target point on the electronic component, and then mounted.
As a result of a diligent study regarding the above-mentioned problems, the inventors of the present invention have concluded that the following are conceivable reasons of profiling errors made by a line sensor.
1. Here is a case of an electronic component 20 such as a Quard Flat Package (QFP) or a Small Outline Package (SOP) equipped with a lead 11 which is electrically conductive and inclined in an elevation or depression angle direction, as shown in FIG. 1.
As shown in FIG. 2A, in the case where a beam of laser light li is projected by a line sensor in a direction which is approximately vertical to the horizontal surface of the lead 11, the reflected light lo diffuses equally in all directions and reaches a detector 21, and therefore it is possible to perform profiling of the shape of the component within the detectable range of the detector 21. On the other hand, in the case where a lead whose surface is mirror-like and the light li is projected on the horizontal surface of the lead 11 with a slight angle onto the surface, as shown in FIG. 2B, the reflected light lo gathers exclusively to one of the detectors 21 and the amount of light exceeds the detectable range of the detector 21. Additionally, the other detector 21 cannot perform profiling of the shape of the component because the amount of light is insufficient. More specifically, this tendency is more noticeable in a lead such as a metal-covered lead with a high reflection rate.
Note that FIGS. 2A and 2B are FIG. 6 is a section views view of the lead 11 in a light projection direction.
2. As shown in FIG. 3A, the light li projected from the line sensor diffuses equally in all directions in the case where the surface of the lead 11 has a satin-like finish or random scars, and thus there is no problem. On the other hand, in the case where the surface of the lead 11 has stripe-shaped scars which are arrayed in a same direction, most of a beam of laser light reflects in a direction perpendicular to these stripe-shaped scars as shown in FIG. 3B. These stripe-shaped scars are called hairlines, and they are considered to be made in manufacturing processing. In the case where a detector 21 is present on the optical axis of the reflected light, the amount of diffused light increases. However, since the increase is within the detectable range of the detector 21, the height of the component can be obtained accurately. In this case, only a small amount of diffused light reaches in the same direction as these hairlines, as shown in FIG. 3C. Thus, in the case where a detector 21 is present in the same direction as the hairlines, the amount of light which reaches the detector 21 is insufficient. Therefore, it is impossible to perform profiling of the shape of the component, or if possible, the accuracy is bad. Additionally, in some cases, these scars face a particular direction with respect to the electronic component, irrespective of the direction in which the lead 11 extends. Therefore, there may be a case where all the shapes of the components cannot be profiled depending on a direction in which the electronic components are supplied.
Note that each of FIGS. 3A, 3B and 3C is a plan view of a part of the lead 11 when viewed in the light projection direction.
3. Here is FIG. 4A shows another case of an electronic component 20 on which pillar-shaped leads 11 extend in the light projection direction of the light li and which are arrayed tightly like a Ceramic Column Grid Array (CCGA), in other words, in the case where the light projection direction of the light li matches the standing direction of these leads 11 and the heights of the leads which reflect the projection light li are greater than the intervals of the standing intervals of the leads 11. In this case, noises n may be measured between the leads 11 in the sweeping direction (the direction of the arrow in FIG. 4B) of the projection light li and the leads 11 in the vertical direction, as shown in FIG. 4B. This occurs when the intervals of these pillar-shaped leads are reduced to a certain level.
In any cases described above, it is impossible to profile the shapes of electronic components accurately. This makes it impossible to recognize a holding misalignment of an electronic component or an electronic component with an abnormal shape in the image processing to be performed later on. Thus, there required to profile the shapes of the electronic component again, or to abandon performing profiling of the three-dimensional shapes of the components and performing profiling of the two-dimensional shapes of the components instead.
The present invention has been conceived considering the above-described problems. An object of the present invention is to recognize a component three-dimensionally irrespective of whether leads of the component are in the above-described state, by using a simple method for preventing a profiling error which occurs in any of these three cases.